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Abstract:

An ion sensitive system has sets of microfluidic microchannels forming
ion sensitive electrodes by the assembly of a substrate with structured
microchannels and another substrate including metal contacts on its
surface. The integrated ion sensitive sensors are each composed of a
microfluidic microchannel to contain an electrolyte, another microfluidic
microchannel to contain the analyte and another microfluidic microchannel
to contain a membrane liquid that separates the electrolyte from the
analyte at the confluent junction of the three solutions. The system has
the dimension of a thin and small disc and can be incorporated in an
analyzing device.

Claims:

1-7. (canceled)

8. Disposable ion sensor system comprising an assembly comprising: a.
first substrate comprising several sets of confluent microfluidic
microchannels integrated at one of its surface, wherein, for each set, a
first of the microfluidic microchannels is designed to draw, by
capillarity, an electrolyte solution, wherein, for each set, a second of
said microfluidic microchannels is designed to draw an analyte solution
between an inlet and an outlet, and wherein, for each set, a third of the
microfluidic microchannels is positioned in between the first and second
microfluidic microchannel and is designed to draw, by capillarity, a
liquid membrane that has the properties of an ionic barrier fluid and
passive valve intended to separate, by surface tension effects, the
electrolyte solution from the analyte solution at the confluent
microfluidic junction between said three microfluidic microchannels, a
second substrate comprising metallic areas deposited on its surface, the
second substrate being assembled to the first substrate so as to close
the microchannels, the metallic areas being superposed to the first
microfluidic microchannels.

9. Disposable ion sensor system according to claim 8 wherein sets of
microfluidic microchannels comprise a fourth microfluidic microchannel
and a fifth microfluidic microchannel to join said second microfluidic
microchannel, which is intended to flow the analyte solution, and wherein
said fourth microfluidic microchannel is designed to draw, by
capillarity, an electrolyte solution and wherein said fifth microfluidic
microchannel is intended to draw, by capillarity, an ionic barrier fluid
that has the function of a passive valve, intended to separate, by
surface tension effects, the electrolyte solution from the analyte
solution at the confluent microfluidic junction between said second,
fourth and fifth microfluidic microchannel, wherein the fifth
microfluidic microchannel is positioned in between said second and fourth
microfluidic microchannel.

10. Disposable ion sensor system according to claim 9 wherein said fourth
and fifth microfluidic microchannel are connected to said second
microfluidic microchannel at a confluent junction position sensitively
different than the location of the confluent junction of the first and
third microfluidic microchannel with said second microfluidic
microchannel.

11. Disposable ion sensor system according to claim 6, wherein the
substrates are made in a polymeric material.

12. Disposable ion sensor system according to claim 9, wherein the
substrates are made in a polymeric material.

13. Disposable ion sensor system according to claim 10, wherein the
substrates are made in a polymeric material.

14. Disposable ion sensor system according to claim 8 wherein the length
of the microfluidic microchannels are in the range of 3-30 mm and their
width in the range of 50-2000 μm, and their depth in the range of
50-1000 μm.

15. Disposable ion sensor system according to claim 9 wherein the length
of the microfluidic microchannels are in the range of 3-30 mm and their
width in the range of 50-2000 μm, and their depth in the range of
50-1000 μm.

16. Disposable ion sensor system according to claim 8 wherein the length
of the microfluidic microchannels are in the range of 2-20 mm and their
width in the range of 60-1000 μm, and their depth in the range of
100-600 μm.

17. Disposable ion sensor system according to claim 9, wherein the length
of the microfluidic microchannels are in the range of 2-20 mm and their
width in the range of 60-1000 μm, and their depth in the range of
100-600 μm.

19. Device according to claim 18 wherein said ion sensor systems are
assembled on top of each other, independent of each other, on a rotatable
axis perpendicular to the plane of said systems connected to an signal
controllable motor.

Description:

TECHNICAL FIELD

[0001] The present invention relates to the field of ion selective
electrodes used in electrochemical systems intended for long term
monitoring of ionic species in an aqueous environment.

BACKGROUND OF THE INVENTION

[0002] In the field of water, waste water, surface and groundwater
monitoring, there is a need for robust, reliable and low cost
electrochemical devices, intended for the protection of water against
agricultural nitrate pollution. For this purpose, ion-selective
electrodes (ISE) have routinely been used for the monitoring of water, to
detect nitrate, chloride, sulfate, and other ions. Most of the ion
selective devices on the market are expensive and are not suited for long
term monitoring. In fact, ion-selective electrodes have a limited
lifetime, due to the degradation of the ion sensing membrane. This is
particularly true in harsh environments, such as encountered in waste
water reservoirs or in riverbeds, where further degradation of the sensor
takes place through bio fouling. Electrodes that are imbedded in such
harsh environments need regular maintenance. Therefore it would be
desirable to replace such electrodes in a simple and convenient way. A
low cost reliable assembly device minimizing the deterioration of the
performance of the measurement system would by highly desirable.

[0003] Disposable solid state sensors possess significant advantages over
conventional ion selective electrodes. The ability to discard the sensors
after several measurement cycles but before they will ultimately fail is
an interesting concept. A number of sensor designs from prior art were
intended to reach this objective.

[0004] Patent CA2100557 describes a disposable ion selective electrode
assembly, for use in analyzers incorporating reference elements and
sensor arrays linearly positioned in parallel on a substrate. In such a
configuration, all the sensors of the array are exposed simultaneously,
with the consequence that their lifetime is limited.

[0005] Patent application US 2009041621, assigned to Kelly et al., is
aimed at monitoring of fluid environments (aqueous and gaseous), and in
particular at devices with anti-bio fouling capabilities deployed in
aquatic environments for the acquisition and monitoring of their chemical
and physical conditions. In order to protect the sensors from bio fouling
formation, the sensors are periodically exposed to a biocide environment
after sampling sequences. This implies the need of an additional biocide
reservoir, which is cumbersome for an autonomous monitoring device.

SUMMARY OF THE INVENTION

[0006] The disadvantages of the ion selective electrode containing devices
described in the foregoing prior art are substantially overcome by the
disposable ion sensor system according to the present invention. This
specification discloses a disposable system comprising ion selective
electrodes realized by the assembly of at least two substrates, of which
one substrate comprises deposited arrays of metallic contacts at one of
its surfaces and which closes, after assembly, a plurality of sets of
fluidic microchannels integrated at the surface of the other substrate,
allowing to flow an electrolyte solution, an analyte solution and an ion
barrier liquid to a confluent junction, where said ion selective liquid
is kept in place by a passive valve and separates the electrolyte
solution from the analyte solution.

[0007] The disposable system disclosed in the present patent application,
comprising a plurality of ion selective electrodes formed by the assembly
of the fluidic substrate and the electrode substrate, allows to be easily
integrated in an analyzing device comprising at least one said system
that can be signal-controllable rotated so that when one ion selective
electrode of the system is being degraded, a signal is generated by the
analyzing device and the degraded ion sensor will be automatically
replaced by a new ion selective sensor and/or reference or
pseudo-reference sensor element present in the system. This routine will
be repeated until all sensors located on the system have been degraded.
The system containing all the ion selective sensors can then be removed
and replaced by a new system. Due to the compactness of the system, which
may present the shape of a compact disc, several systems comprising each
a plurality of ion selective electrodes can be easily assembled with a
high density.

[0008] Other details of the invention will be found in the set of claims
and are described hereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The nature, advantages and various additional features of the
invention will appear more fully upon consideration of the illustrative
embodiments in the accompanying drawings:

[0010] FIG. 1 illustrates a top view of microfluidic microchannels
integrated on a fluidic substrate;

[0011] FIG. 2 illustrates an enlarged view of three microfluidic
microchannels at their confluent junction on a fluidic substrate;

[0013] FIG. 4 shows another enlarged view of three confluent microfluid
microchannels with incorporated microstructures at their confluent
junction on a fluidic substrate;

[0014] FIG. 5 illustrates a geometry of a cross sectiongeometries of
microstructures integrated at the junction between three microfluidic
microchannels on a fluidic substrate;

[0015] FIG. 6 shows a detailed view of a microfluidic microchannel
structure intended to realize two ion sensitive sensors formed in
junction with a single analyte microchannel;

[0016] FIG. 7 illustrates a top view of a fluidic substrate;

[0017] FIG. 8 shows a top view of a substrate with deposited metal
contacts;

[0018] FIG. 9 shows a side view of a fluidic substrate and a substrate
with deposited metal contacts;

[0019] FIG. 10 shows a device allowing to rotate a system comprising a
plurality of ion selective electrodes; and

[0020] FIG. 11 shows another device with different systems comprising ion
selective electrodes assembled on top of each other.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] According to a preferred embodiment of the invention, a disposable
ion sensor system comprises two substrates.

[0022] A first substrate,
called fluidic substrate 6, presents a set of microchannels integrated on
its surface which are intended to draw, by capillarity, an electrolyte
solution and a liquid membrane at a confluent junction of said
microchannels. The analyte solution(s) will be either pumped through the
channel 2 or drawn by capillarity. As it will be outlined in more details
further, the purpose of the liquid ion-selective membrane, called
hereafter also membrane, is to act as an ion barrier that separates the
analyte solution from the electrolyte solution at their confluent
junction.

[0023] A second substrate, called the electrode substrate 7,
presents deposited metal contacts on one of its surfaces, opposite to the
first substrate.

[0024] After assembly of the two substrates and filling of the
microchannels 1 and 3, as it will be explained hereafter, the system will
contain completely formed ion selective electrodes.

[0025] FIG. 1 illustrates a configuration of surface microstructures of
the fluidic substrate of the preferred configuration. A first
microfluidic microchannel, called electrolyte microchannel 1, is sized to
be able to draw, by capillarity, an electrolyte solution from an outside
reservoir containing a known electrolyte solution, through an inlet 10. A
second microfluidic microchannel, called the analyte channel 2, is
intended to draw, by capillarity or active pumping, an analyte solution
from an inlet 22 to an outlet 24. A third microfluidic microchannel,
called membrane microchannel 3, is intended to draw, by capillarity, a
liquid ion-selective membrane, and comprises an inlet and is
advantageously positioned in between said electrolyte microchannel 1 and
said analyte microchannel 2. FIG. 2 illustrates a typical geometry of the
confluent junction of the analyte microchannel 2, the electrolyte
microchannel 1 and the membrane microchannel 3.

[0026] Membrane microchannel 3 and electrolyte microchannel 1 may present
each a curved extremity in the region of the confluent junction. Membrane
microchannel 3 is designed so that its curved extremity is connected, by
an opening, to the curved extremity of the electrolyte microchannel 1.
The common extremities of the electrolyte microchannel 1 and the membrane
microchannel 3 form at that confluent location a single channel that is
further connected to an opening at one of the sides of the analyte
microchannel 1. A typical diameter of said opening is between 0.1 μm
to 200 μm, preferably between 1 μm to 20 μm.

[0027] By capillarity effects, the liquid membrane can be drawn from the
inlet 30 of the membrane microchannel 3 to the common confluent junction
with said analyte microchannel 2 and said electrolyte microchannel 1. The
liquid membrane is prevented to draw in the microchannel 1 and in the
microchannel 2 by an abrupt change of the geometry of the channel as
shown in FIG. 3 that leads to an abrupt change of the contact angle of
the liquid membrane and the surface of the liquid membrane microchannel.
Once the liquid membrane is held in place by surface tension effects at
the common junction of said three microchannels, it will separate the
electrolyte solution from the analyte solution because the electrolyte
solution and analyte solution are immiscible with the liquid membrane.
One of the surfaces 32 of the liquid membrane in said confluent junction
will remain in contact with the electrolyte solution without fluidic
exchange, while the other surface 31 of the membrane liquid in said
confluent junction will remain in contact with the analyte solution
without fluidic exchange.

[0028] In the system, at the contact surface 31 of the analyte solution
with the liquid membrane, ions will be exchanged at said contact surface
31, producing as such an electrical potential which value is proportional
to the ion content of the analyte.

[0029] The electrochemical properties and mechanism of a liquid membrane
are well known to a person skilled in the art. The liquid membrane has an
advantageously chosen chemical composition and property for a specific
ion-selective electrode. Its properties are based on the use of
ionophores and lipophilic substances solubilized in the said liquid
membrane. The ionophore in the liquid membrane allows the analyte ion to
solubilize in the liquid membrane and an equilibrium of the analyte ion
to be achieved at the interface of the analyte and the liquid membrane.

[0030] A great variety of compositions of liquid membranes can be used and
are chosen in function of the analyte solution, the electrolyte solution,
the desired surface tension properties of the deployed solutions and also
the flow properties of said liquid membrane. The form of the curved part
14 of the electrolyte microchannel and the curved part 15 of the membrane
microchannel are also advantageously determined so as to assure a smooth
flow of the electrolyte and membrane liquid and to avoid that said fluids
do not mix at their confluent junction using an advantageously chosen
geometry.

[0031] In order to explain the detailed geometry of the three dimensional
structures and connection of the analyte microchannel 2, the electrolyte
microchannel 1 and the membrane microchannel 3, several cross sections
through the confluent junction of said three microchannels are shown in
FIG. 3. In a variant design of the first embodiment, microstructures 38
can be integrated at the confluent junction of the liquid membrane and
the analyte solution, as illustrated in FIG. 4. The microstructures 38
are intended to improve the positional and shape stability of the
membrane liquid at that area. FIG. 5 illustrates a cross section 39 of
such a microstructure, perpendicular to the plane of the liquid
substrate. Different other geometries and positions of such an array of
microstructures can be realized in the confluent region of the three
fluidic micro channels. For example the microstructures can be positioned
closer to the electrolyte microchannel, or several arrays of said
microstructures can be organized in said confluent area. Preferably said
microstructures 38 have a triangular shape in the plane of the fluidic
substrate. The stabilizing microstructures can have any type of cross
section perpendicular to the plane of the fluidic substrate, preferably a
semi disc shaped cross section, so that the liquid membrane will stop at
the interface between micro channels 3 and 2.

[0032] In order to realize complete ion selective sensors another
substrate, called electrode substrate 7, is conveniently structured. As
shown in FIG. 8, it comprises deposited metallic contacts 8 on its
surface, which are positioned so that they will be aligned and come in
contact and close said electrolyte micro channels 1 after assembly with
said fluidic substrate 6. Preferably the length of the deposited metallic
contacts 8 will be chosen as long as possible and sensitively similar to
the length of the electrolyte microchannel 2, this in order to maximize
the stability and sensitivity of the signal to be measured. Complete
ion-selective electrodes are formed at the end of the assembly process of
the liquid substrate 6 with the electrode substrate 7, which surface
comprising the deposited metal contacts closes completely the
microfluidic microchannels and allow as such flow of fluids in their
corresponding closed microchannels.

[0033] FIG. 9 illustrates a side view of said liquid substrate 6 shown in
FIG. 7, and said electrode substrate 7 shown in FIG. 8.

[0034] Once the assembly of the liquid substrate 6 with electrode
substrate 7 is performed, the assembled system is ready for introduction
of liquids in their corresponding microchannels through their
corresponding inlets.

[0035] The invention allows for different sequenced steps of the
introduction of the liquids in their corresponding microchannels. In a
preferred sequence of the introduction of fluids in corresponding
microchannels, the electrolyte solution and analyte solution are
introduced in their respective microchannels so that each comes in
contact with the stabilized membrane fluid at the confluent junction by
their respective contact surfaces 31 and 32. Thereafter the membrane
liquid is first introduced in the membrane microchannel 3, through its
inlet 30 and drawn, by capillary effects at the confluent junction of the
three said microchannels and will remain fixed at said confluent junction
by surface tension effects. The internal electrolyte will stop at the
interface surface 32 of the membrane microchannel 3 by surface tension
effects. After the introduction of the analyte solution in the analyte
microchannel 2, the analyte solution will not mix with the liquid
membrane because of the hydrophobic properties of the liquid membrane and
measurements of specific ion contents of the analyte can start. Different
variants of the liquid introduction sequence procedure can be imagined.
Prior to the start of the analysis of the analyte, a calibration solution
can be flown through the analyte microchannel and a calibration
measurement is performed.

[0036] In another preferred embodiment of the invention at least one more
ion selective sensor can be formed by another confluent connection of two
microfluidic microchannels to the analyte microchannel 2. FIG. 6
illustrates a design allowing to realize two ion selective sensors for
the same analyte microchannel 2, allowing as such the simultaneous
measurement of two different ions in the analyte or to average the
results of the measurement of one ion species in order to get a better
accuracy. Alternatively, one of the ion-selective sensors could be used
as reference channel, working as a reference or pseudo-reference
electrode.

[0037] In order to achieve this configuration, a micro channel 4, intended
to flow an identical or another electrolyte solution than the one
introduced in microchannel 1, is integrated and separated from analyte
microchannel 2 by a membrane microchannel 5. The position 33 of the
confluent junction of the analyte microchannel 2 and the second membrane
microchannel 5 is sensibly different than the junction location 31 of the
first set of microchannels. It should be understood that the invention is
not limited to the integration of 2 ion sensors for each analyte
microchannel. Also, different variations of the geometries of the set of
microchannels illustrated in FIGS. 1 and 2 are possible.

[0038] Ion selective sensors can be organized in a radial direction or in
any other layout in said system. Also, a single system can comprise a
wide variety of different possible organizations and types of ion
selective sensors. In a standard system adjacent ion sensors detect
different ion species. In another configuration several adjacent ion
sensors detect the same ion and a next one ion sensor is designed to
detect another species of ion. There is no limitation in the combination,
positioning, size or numbers of the sensors in the system. It should be
understood that the sets of fluidic microchannels can be oriented in a
different way than the one illustrated in FIG. 7. The set of
microchannels constituting ion selective sensors can be distributed in
different ways than the circular and axial symmetric distribution shown
in FIG. 7

[0039] A great number of ion selective sensors can be integrated in a
system. Preferably 10 to 100 ion selective sensors can be integrated. A
typical length of the electrolyte microchannel 1 is between 2 mm to 20
mm, preferably 3 mm to 15 mm. A typical depth of the microchannel 1 is
0.1 mm to 1 mm, preferably 0.2 mm to 0.5 mm. Typical width of
microchannel 1 is between 0.1 mm and 1.2 mm, preferably between 0.3 mm
and 1 mm.

[0040] A typical length of the analyte microchannel 2 is between 2 mm to
50 mm, preferably 5 to 30 mm. Typical depths of the micro channel 1 is
0.1 mm to 1 mm, preferably between 0.3 mm and 0.6 mm. Typical width of
microchannel 1 is between 0.3 mm and 2 mm, preferably between 0.5 mm and
1 mm.

[0041] A typical length of the membrane microchannel 1 is between 2 mm to
20 mm, preferably 3 to 15 mm. Typical depths of the microchannel 1 is
0.05 mm to 0.3 mm, preferably between 0.1 mm and 0.2 mm. Typical width of
microchannel 1 is between 0.05 mm and 0.3 mm, preferably between 0.06 and
0.2 mm.

[0042] Typical diameter of the inlets and outlets are between 0.5 and 1.5
mm, preferably between 0.8 and 1.2 mm. Typical mutual separation
distances between the inlets 10, 20, 30 are between 4 mm to 30 mm,
typically between 5 to 15 mm.

[0043] Typical width and lengths of the metal contacts are similar to the
ones of the electrolyte microchannels and the thickness of the deposited
metal is typically 0.1 to 2 μm, preferably 0.2 to 0.5 μm.

[0044] The fluidic substrate and the electrode substrate that form the
disposable system can both be made for instance by hot embossing or by
injection molding techniques or by classical precision milling. The used
material of both substrates is preferably a polymeric material that can
withstand high temperature, humidity changes and solvents. COO (cyclic
olefin copolymer) is such a material, other material such as COP, PMMA,
PC, PEEK or other similar polymer could be used as well. COC is well
suited since it resists very well solvent such as cyclohexanone and THF,
often used in ion-selective membrane solutions.

[0045] The fluidic substrate and the electrode substrate can be assembled
by different well known techniques. For example they can be assembled by
thermal bonding or glued using an adhesive layer, or by using a glue
layer deposited on one of the substrates. The metallic contacts of the
electrode substrate of the electrochemical sensors are either screen
printed, evaporated, sputtered and/or electrodeposited on the polymeric
substrate 7 and their thickness is advantageously chosen to be very thin,
preferably 1 μm, in order to allow to close the fluidic microchannels
without risk of leakage.

[0046] Once the system comprising ion selective sensors is formed it can
be integrated in different ways in an analyzing device.

[0047] In an application of the invention the disposable system 28, which
may have the size and shape of a typical compact disc having a diameter
of typically 10 cm and typical thickness of 1-2 mm, is integrated in a
device comprising a signal controllable motor 16 that allows to rotate
the disposable system. FIG. 10 illustrates the concept of such a device.
The device comprises a motor 16, preferably a step motor, a platform on
which the system is fixed and advantageously chosen connectors to
introduce, without leakage, liquids in their corresponding inlet and
outlets of the micro channels. A container 23 is provided in order to
collect the waste analyte solution. Once the measurement is performed,
the signal is treated by a computer 17. If the measurement performed with
the calibration solutions fails, or after a given number of sample
injections, then a signal is sent to the motor, which turns the
substrate, so that the next sensor faces the inlet solution.

[0048] Several variants of this aspect of the invention are possible. For
instance, calibration solutions 18 can be introduced in the system via a
distributor, prior to the first measurement. Then the distributor is
switched and a sample measurement can be performed. The calibration 18 or
the sample solution 19 flows in the disposable cartridge through a
microchannel in which one or more sensors are integrated. A reference
electrode 21 can either be integrated directly on the substrate or in the
distributor as illustrated in FIG. 10.

[0049] It should also be pointed out that the present system and also its
device could contain at least one humidity and at least one temperature
sensors.

[0050] In order to protect the inlets and outlets of the ion selective
sensors integrated in the system, before their use, a thin polymer layer
may be deposited on one face of the system at the side of the inlets and
outlets of the microfluidic microchannels. The system can be imbedded in
a protective environment. If needed, a mechanical system is provided to
open and remove the thin protective polymer layer facing the inlet and
outlets before the ion selective sensor has to be activated. Also, when
the ion selective sensor has been positioned in its new place ready to
perform measurements, a mechanical system brings a fluidic tubing
comprising a fluidic connector in contact with the inlets and outlets of
the set of the microfluidic microchannels of said ion selective sensor.

[0051] In a further embodiment of the invention, advantage is taken from
the size and shape of the ion sensor system and several said systems 25,
26, 27 are assembled on top of each other in a device as shown in FIG.
11. The assembly of the different systems is designed such that each
system can be rotated individually by an advantageously chosen mechanical
system in which the individual rotation of the systems can be controlled
by signals coming from the active ion sensors and which are treated by a
computer 17 who drives the rotation of the individual systems. Different
variants of the assembly of the disc shaped systems can be possible. In a
preferred arrangement, illustrated in FIG. 12 the system discs comprise a
radial slot 29 opened at the periphery of said system discs along a
radius of the system so that the system can be removed laterally from the
device. An advantageously chosen mechanical system could perform this
operation automatically and assure its replacement by the introduction of
a new system in the device.